2 research outputs found
Robust Extraction of Hyperbolic Metamaterial Permittivity Using Total Internal Reflection Ellipsometry
Hyperbolic metamaterials
are optical materials characterized by
highly anisotropic effective permittivity tensor components having
opposite signs along orthogonal directions. The techniques currently
employed for characterizing the optical properties of hyperbolic metamaterials
are limited in their capability for robust extraction of the complex
permittivity tensor. Here we demonstrate how an ellipsometry technique
based on total internal reflection can be leveraged to extract the
permittivity of hyperbolic metamaterials with improved robustness
and accuracy. By enhancing the interaction of light with the metamaterial
stacks, improved ellipsometric sensitivity for subsequent permittivity
extraction is obtained. The technique does not require any modification
of the hyperbolic metamaterial sample or sophisticated ellipsometry
setup and could therefore serve as a reliable and easy-to-adopt technique
for characterization of a broad class of anisotropic metamaterials
Infrared Nanoimaging of Hydrogenated Perovskite Nickelate Memristive Devices
Solid-state devices
made from correlated oxides, such as perovskite
nickelates, are promising for neuromorphic computing by mimicking
biological synaptic function. However, comprehending dopant action
at the nanoscale poses a formidable challenge to understanding the
elementary mechanisms involved. Here, we perform operando infrared nanoimaging of hydrogen-doped correlated perovskite, neodymium
nickel oxide (H-NdNiO3, H-NNO), devices and reveal how
an applied field perturbs dopant distribution at the nanoscale. This
perturbation leads to stripe phases of varying conductivity perpendicular
to the applied field, which define the macroscale electrical characteristics
of the devices. Hyperspectral nano-FTIR imaging in conjunction with
density functional theory calculations unveils a real-space map of
multiple vibrational states of H-NNO associated with OH stretching
modes and their dependence on the dopant concentration. Moreover,
the localization of excess charges induces an out-of-plane lattice
expansion in NNO which was confirmed by in situ X-ray
diffraction and creates a strain that acts as a barrier against further
diffusion. Our results and the techniques presented here hold great
potential for the rapidly growing field of memristors and neuromorphic
devices wherein nanoscale ion motion is fundamentally responsible
for function